1. Field of the Invention
This invention relates to a process for forming integrated circuit structures. More particularly, this invention relates to a process for forming a layer of low dielectric constant (low k) dielectric material in an integrated circuit structure.
2. Description of the Related Art
The shrinking of integrated circuits has resulted in levels of electrically conductive interconnects being placed closer together vertically, as well as reduction of the horizontal spacing between the electrically conductive interconnects, such as metal lines, on any particular level of such interconnects. As a result, capacitance has increased between such conductive portions, resulting in loss of speed and increased cross-talk. One proposed approach to solving this problem of high capacitance is to replace the conventional silicon oxide (SiO2) dielectric material, having a dielectric constant (k) of about 4.0, with another insulation material having a lower dielectric constant to thereby lower the capacitance.
In an article by L. Peters, entitled xe2x80x9cPursuing the Perfect Low-K Dielectricxe2x80x9d, published in Semiconductor International, Volume 21, No. 10, September 1998, at pages 64-74, a number of alternate dielectric materials are disclosed and discussed. Included in these dielectric materials is a description of a low k dielectric material having a dielectric constant of about 3.0 formed using a Flowfill chemical vapor deposition (CVD) process developed by Trikon Technologies of Newport, Gwent, U.K. The process is said to react methyl silane (CH3xe2x80x94SiH3) with hydrogen peroxide (H2O2): to form monosilicic acid which condenses on a cool wafer and is converted into an amorphous methyl-doped silicon oxide which is annealed at 400xc2x0 C. to remove moisture. The article goes on to state that beyond methyl silane, studies show a possible k of 2.75 using dimethyl silane in the Flowfill process.
An article by S. McClatchie et al. entitled xe2x80x9cLow Dielectric Constant Oxide Films Deposited Using CVD Techniquesxe2x80x9d, published in the 1998 Proceedings of the Fourth International Dielectrics For ULSI Multilevel Interconnection Conference (Dumic) held on Feb. 16-17, 1998 at Santa Clara, Calif., at pages 311-318, also describes the formation of methyl-doped silicon oxide by the low-k Flowfill process of reacting methyl silane with H2O2 to achieve a dielectric constant of xcx9c2.9.
The incorporation of such carbon-doped silicon oxide dielectric material into interconnect architecture has been very attractive not only because of the low k properties, but also because of the compatibility with conventional silicon process technologies. Generally these materials remain stable upon annealing; at temperatures of up to 500xc2x0 C. The carbon doped silicon oxide materials are characterized by the structure of amorphous silicon oxide with incorporated methyl groups and hydrogen species, and are also characterized by a reduced density in comparison with conventional silicon oxide that can be explained by the formation of microporosity surrounding the incorporated methyl groups. Furthermore, such hydrocarbon-modified silicon oxide dielectric materials deposited by CVD techniques are also characterized by strong adhesion.
The above discussed reaction of methyl silane and hydrogen peroxide has been found to result in the formation of a low k Carbon-containing silicon oxide dielectric material with excellent fill properties in high aspect ratio regions of an integrated circuit structure such as between closely spaced apart metal lines or in narrow isolation trenches. However, it has been found that the reaction rate between the reactants must be controlled so that it is neither too slow or too fast. If the reaction is too slow, an uneven reaction appears to occur across the surface of the substrate. The results also appear to be apparatus sensitive, i.e., with results differing from one reaction chamber to another.
On the other hand, if the reaction is too fast, the result is pressure spiking wherein momentary pressure bursts can cause poor: across-wafer thickness uniformity of the deposited film, as well as a xe2x80x9chazexe2x80x9d or condensation problem. In the aforementioned Sukharev U.S. patent application Ser. No. 09/274,254, it is stated that the pressure spikes sometimes are high enough to actually stop the reaction by increasing the pressure in the reaction chamber sufficiently to interfere with the flow of reactants into the chamber. Sukharev further states that such pressure spiking and resultant rise in pressure can result in the precipitation of particles of the reaction product in the gas phase and their subsequent deposition on the substrate surface.
Sukharev stated that pressure spiking could be avoided by varying the CH3SiH3/H2O2 concentration ratio and/or total flows, but that the multi-factor character of such optimization would make it difficult to develop reliable technology by means of the process parameter variations only.
Sukharev then proposed to control the reaction rate between the carbon-doped silane and the peroxide oxidizing agent by the addition of one or more reaction-retarding additives such as an inorganic compound selected from the group consisting of: Cl2, Br2, I2, HF, HCl, HBr, HI, N2, NO, NO2, N2O, H2S, CO, CO2, NH3, SO2, H2, Kr, Ar, Ne, and He; an organic compound selected from the group consisting of: a 1-6 carbon alkane, a 1-6 carbon alkene, a 1-6 carbon alkyne, a 1-6 carbon alcohol, a 1-6 carbon aldehyde, a 1-6 carbon ketone, a 1-6 carbon carboxylic acid, a 1-10 carbon aromatic, and any of the above organic compounds having one or more atoms therein selected from the group consisting of F, Cl, Br, I, S, N, and P; and mixtures of any 2 or more of the above.
It, therefore, remains desirable to provide for control of the reaction rate of the carbon-doped silane with the peroxide oxidizing agent used to form low k carbon-doped silicon oxide dielectric material so that the reaction rate is neither too fast or too slow.
Control of a reaction between a peroxide oxidizing agent and a carbon-substituted silane to form a low k carbon-containing silicon oxide dielectric material is achieved, in a first embodiment, by adding, to the carbon-substituted silane reactant, unsubstituted silane (SiH4), to accelerate the process for forming a low k carbon-containing silicon oxide dielectric material by reaction of the carbon-substituted silane/unsubstituted silane mixture with hydrogen peroxide.
In a second embodiment, control of a reaction between a peroxide oxidizing agent and a reactant mixture comprising carbon-substituted silane and unsubstituted silane to form a low k carbon-containing silicon oxide dielectric material is achieved by controlling the ratio of the flow of the hydrogen peroxide reactant and the flow of the reactant mixture of carbon-substituted silane and unsubstituted silane into a reaction chamber though structural modification of the faceplate of the showerhead through which the reactants flow into the chamber.